Seat cushions, and in particular motor-vehicle seat cushions, generally comprise a reinforcement formed by a frame inside which there is mounted a layer of tensioning wires intended to support padding. The tensioning wires are most often bent in a zigzag between the two opposite sides of the frame, but are arranged parallel to one other. If they are not joined together, they have the tendency, after a certain period of use, to move apart and to make the seat too soft.
They are therefore often joined together, as described in No. FR-A-1,282,875, by means of cross-members which are hooked onto straight parts of the successive wires. However, the positioning of these members calls for a special hooking tool, which is very costly and requires a relatively large amount of time.